Bucket tip/collection slot combination for open-circuit liquid-cooled gas turbines

ABSTRACT

Bucket tip designs are shown for manifolding fluid discharge from open-ended coolant passages in a liquid-cooled gas turbine. The manifolded fluid (e.g., steam and excess water in a watercooled system) is discharged from the trailing edge of the bucket and liquid content thereof is thrown into a collection slot located in register therewith in the wall of the casing.

United States Patent 1 Kydd [ 51 May 29, 1973 BUCKET TIP/COLLECTION SLOTCOMBINATION FOR OPEN-CIRCUIT LIQUID-COOLED GAS TURBINES Paul H. Kydd,Scotia, N.Y.

General Electric Schenectady, NY.

Filed: Nov. 27, 1970 Appl. No.: 93,057

Inventor:

[73] Assignee: Company,

U.S.Cl. ..4l6/97,416/2l7,4l5/168 Int. Cl ..F0ld 5/18 Field of Search..416/90, 91, 92, 93, 416/95, 96, 97, 215, 217, 219, 232; 415/168, 116;60/3966 References Cited UNITED STATES PATENTS 10/1970 Kercher ..4 16/92 8/1958 Hayes ..4 1 6/90 5/1969 Kydo ..4l6/232 10/1970 Palfreyman..4 1 6/2 1 7 FOREIGN PATENTS OR APPLICATIONS 386,276 12/1923 Germany..60/39.66

726,545 1/1931 France ..4l5/l 15 586,838 4/1947 Great Britain 588,24312/1959 Canada 383,506 5/1920 Germany....

346,599 l/1922 Germany ..60/39.66

Primary Examiner-Everette A. Powell, Jr. Attorney-Richard R. Brainard,Paul A. Frank, Charles T. Watts, Leo I. Malossi, Frank L. Neuhause'r,Oscar B. Waddell and Joseph B. Forman [57] ABSTRACT Bucket tip designsare shown for manifolding fluid discharge from open-ended coolantpassages in a liquid-cooled gas turbine. The manifolded fluid (e.g.,steam and excess water in a water-cooled system) is discharged from thetrailing edge of the bucket and liquid content thereof is thrown into acollection slot located in register therewith in the wall of the casing.

5 Claims, 6 Drawing Figures PATENTH) HAYZ 9 I975 SHEET 8 BF 3 a $2M M SBUCKET TIP/COLLECTION SLOT COMBINATION FOR OPEN-CIRCUIT LIQUID-COOLEDGAS TURBINES BACKGROUND OF THE INVENTION Structural arrangements for theliquid cooling of gas turbine buckets are shown in U. S. Pat. Nos.3,446,481 Kydd and 3,446,482 Kydd. These patents are incorporated byreference.

The provisions for open-circuit liquid cooling disclosed therein areparticularly importantfor the capability offered thereby for increasingthe turbine inlet temperature to an operating range of from 2,500 F toat least 3,500 F thereby obtaining an increase in power output rangingfrom about 100 to 200 percent and in an increase in thermal efficiencyranging to as high as 50 percent. Such open-circuit liquid-cooledturbine structures are referred to as ultra high temperature gasturbines.

One problem arising in the operation of an unshrouded open-circuitliquid-cooled turbine in which there is a sizeable reaction at thebucket tip is that there is a substantial pressure difference (a) frominlet to outlet of the gas path (i.e., from bucket leading edge tobucket trailing edge] in the bucket tip region, (b) from one side of thebucket to the other and (c) from the root to the tip. The coolantpassages shown in the Kydd patents extend radially of the buckets frombelow the surface of the platforms to the distal ends thereof and areopen at both ends. During operation these coolant passages do not runfull of liquid coolant due to centrifugal and coriolis forces. Theproblem that presents itself and that is solved by the instant inventionis that since all of these coolant passages open at the inner endsthereof into a region of common pressure, when the outer ends of all ofthese same coolant passages open to the local ambient pressure atvarious locations around the bucket tip, hot gas will flow into some ofthese passages and this is hightly undesirable.

Although the problem can be minimized by making the tip clearance smallenough, liquid coolant will pile up at the tip under certain conditionsintroducing an unwanted braking action and creating erosion problems. Itwould moreover be desirable to maintain tight clearances at the buckettips.

SUMMARY OF THE INVENTION The instant invention provides a solution tothe aforementioned problems while enabling operation of an open-circuitsystem with tight tip clearances at adequate liquid coolant flow. Allthe coolant passages are manifolded at each bucket tip placing a barrierbetween the open ends of the coolant passages and the hot gas stream andthe hot colling fluids are redirected and discharged at the trailingedges of the buckets whereby liquid content thereof is thrown into anannular collection slot in register therewith in the casing wall tofacilitate collection and recireculation of excess liquid coolant.

BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention aswell as objects and advantages thereof will be readily apparent fromconsideration of the following specification relating to the annexeddrawings in which:

FIG. 1 is a three-dimensional view partially cut-away to display anopen-circuit liquid-cooled turbine bucket having the manifolding anddischargeprovision of this invention;

FIG. 2 shows the manifolding and discharge features of this invention incombination with the annular collection slot;

FIG. 3 is a section taken on line 33 of FIG. '2;

FIF. 4 is a section taken on line 4-4 of FIG. 2;

FIG. 5 is an offset section taken on line 55 of FIG. 3 and FIG. 6 is asecond embodiment of the combination shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT] Turbine bucket 10 consists of asheet metal skin 11 affixed (e.g., by brazing) to investment cast hollowcore 12 having integral spanwise extending grooves 13a formed therein.The rectangular cooling channels, or passages, 13 defined by skin 11 andgrooves 13a conduct cooling liquid therethrough at a uniform depthbeneath skin 11. At the upper ends thereof the rectangular coolingchannels 13 on the pressure side of bucket 10 are in flow communicationwith and terminate at manifold 14, which is shown recessed into core 12.Manifold 14 (and, thereby, channels 13) is separated from the tip ofbucket 10 by the wall portion 12a of core 12 extending chordwisethereof. On the suction side of bucket 10 rectangular cooling channels13 are in flow communication with and terminate at manifold 14a recessedinto core 12. A suction side wall portion (not shown) similar to wallportion separates manifold 14a from the tip of bucket 10. Near thetrailing edge of bucket 10 the cross-over conduit 15 connects manifold14a to manifold 14. Crossover 15 and the relation between manifolds 14,14a is best seen in FIG. 4.

Requisite open-circuit cooling from manifolds 14, 14a is insured by thepresence of opening 16, which provides for the exit of the heatedcooling fluids (gas or vapor and excess liquid coolant) from manifold 14at the trailing edge of bucket 10 as shown. Annular collection slot 17formed in casing 18 receives the centrifugally directed ejected fluidfor the eventual recirculation or disposal thereof.

By using this provision for manifolding and collecting of the coolant,the bucket tip/casing clearance can be made close and any excess liquidpassing through bucket 10 will be thrown clear of the bucket intocollection slot 17 avoiding any braking effect therefrom.

The trailing edge of the core 12 near the top is provided with coolingchannels 13 on the pressure side only due to the thinness of thesection. Several of the trailing edge cooling channelson the suctionside are brought together at some point below manifolds 14, 14a.

The root end of core 11 consists of a number of finget-like projections,or tines, 19 of varying length. These tines 19 may present a generallyrectangular profile as shown or each tine may be tapered toward thedistal end thereof to present a generally triangular profile. Rim 21 ofturbine disk 22 has grooves 23 machined therein extending to variousdepths and having widths matching the different lengths and widths ofbucket tines 19 such that tines 19 will fit snuggly into the completedgrooves 23 in an interlocking relationship. Triangularly shaped buckettine profiles provide for improved stress distribution of shear stressesin the joints between tines l9 and the walls of grooves 23 and oftensile stresses within the tines themselves.

Once the proper fit has been obtained, the appropriate amount of brazingalloy is placed in each groove 23 and the buckets are inserted and heldin fixed position by a fixture. This fixture is biased to maintain atight fit between tines 19 and grooves 23 regardless of thermalexpansion. Conventional brazing alloys having melting points rangingfrom 700 to l,lO C may be used. Single metals, such as copper, may alsobe used. This interlocking bucket/rotor disk construction is morecompletely described and claimed in U. S. Pat. application Ser. No.93,058 Kydd (incorporated by reference), filed Nov. 27, 1970 (nowabandoned) and assigned to the assignee of the instant invention.

Thereafter, the assembly (the rim with all the buckets properly located)is furnace-brazed to provide an integral structure.

Steel alloys may be used for the skin and core, preferably thosecontaining at least 12 percent by weight of chromium for corrosionresistance and heat treatable to achieve high strength.

The cutting of grooves 23 into rim 21 not only provides the requisiteconfiguration for fastening the bucket root and lessens the weight ofthe rim, but in addition the ribs 24 between grooves 23 provide area onthe upper surfaces thereof for attachment thereto of platform elements26 having cooling channels 27 and 28 formed therein. The coolingchannels 27 are in juxtaposition with grooves 23 and cooling channels 28interconnect the cooling channels 27 as shown. The separating walls 29between cooling channels 27 are dimensioned to coincide with the widthof juxtaposed ribs 24.

In preparing platform elements 26 the distal face of each wall 29 isground to a radius common to the outer diameter of ribs 24 to enable theelectron beam welding, or brazing, of separating walls 29 to the ribs24. Similarly, the distal face of each edge rib 31 is accurately groundto the radius of the outer diameter of the ribs 24 so that ribs 31 willprovide a cylindrical surface facing radially inward, the elements ofwhich extend in the axial direction. These cylindrical surfaces arepresented alongside bucket on each side thereof adjacent the coolingchannels 13. In operation these distal faces of edge ribs 31 willfunction as weirs over which the cooling fluid can distribute uniformlyinto the grooves 13a leading to bucket cooling channels 13 of eachbucket.

This weir construction, which is critical to effective metering of thecoolant to the buckets is more fully described and is claimed in U. S.Pat. application Ser. No. 93,056 Kydd (incorporated by reference) filedNov. 27, 1970 (US. Pat. No. 3,658,439) and assigned to the assignee ofthe instant invention. As is explained therein all portions of thosecylindrical surfaces receiving coolant from a common distribution pathmust be accurately located equidistant from the axis of rotation.

As is described in the aforementioned Kydd patents, cooling liquid(usually water) is sprayed at low pressure in a generally radiallyoutward direction from nozzles (not shown but preferably located on eachside of disk 22) and impinges on disk 22. The coolant thereupon movesinto gutters 32, 32a defined in part by downwardly extending lipportions 33, 33a. The cooling liquid accumulates in gutters 32, 32a(cooling the rim portions with which it comes into contact) beingretained therein until this liquid has been accelerated to theprevailing disk rim velocity.

After the cooling liquid in gutters 32, 32a has been so accelerated,this liquid continually drains from gutters 32, 32a passing radiallyoutward through holes 34, 34a of which holes 34 are in flowcommunication with the two outside grooves 23 (FIGS. 2 and 4) in theregions between buckets 10. As is shown in the aforesurfaces of theplatform elements 26, these elements I are kept cool. Thereafter, thecoolant passes over the distal faces of edge ribs 31 in thin sheets intothe radially inner ends of cooling channels 13 (via grooves 13aprojecting below the lower end of skin 11) in adjacent buckets l0 andthence into and through the turbine buckets.

As the cooling liquid moves through cooling channels 13 of any givenbucket 10 a large portion (or substantially all of the cooling fluid,depending upon the rate of flow) is converted to the gaseous or vaporstate as it absorbs heat from the skin 11 and core 12 of the bucket. Atthe outer ends of cooling channels 13 the vapor or gas generated and anyremaining liquid coolant pass into manifolds 14 and 14a and isredirected to exit from the manifold system via opening 16 intocollection slot 17 to complete the open-circuit cooling path.

FIG. 6 sets forth a modification of this invention wherein the fluiddischarge is effected radially outward via hole 41 into annularcollection slot 42. In this embodiment as well the cross-over passage 15is used to convey the fluid from manifold 14a to manifold 14 in flowcommunication with slot 42. Wall portion 12b (and a similar wallportion, not shown, on the suction side) functions in the same way aswallportion 12a serving to set apart the discharge ends of channel 13from the hot gas stream and to direct the coolant flow to hole 41 fordischarge therefrom.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a gas turbine wherein a turbine disk is mounted on a shaftrotatably supported in a casing, said turbine disk extendingsubstantially perpendicular to the axis of said shaft and having turbinebuckets and platform means affixed to the outer rim thereof, saidbuckets receiving a driving force from a hot motive fluid confinedwithin said casing and moving in a direction generally parallel to saidaxis of said shaft and the driving force being transmitted to said shaftvia said turbine disk, means located radially inward of said platformadjacent said turbine disk for introducing liquid coolant within saidturbine in a radially outward direction into opencircuit distributionpaths by which said coolant traverses surface area of said rim and saidplatform means, passes into cooling channels in said buckets and exitsfrom said channels in a radially outward direction, th

- improvement comprising:

each bucket in flow communication with the discharge ends of the coolantchannels, said first and second manifolds being located on the pressureand suction sides of said bucket, respectively,

2. a single opening through the blade structure interconnecting saidfirst manifold and the region of hot motive fluid flow within the casingnear the trailing edge of said bucket, each of said manifolds beingseparated from the tip of said bucket by a wall formed in the bucketstructure on the radially outward side of said manifold and extendinggenerally chordwise of said bucket whereby coolant discharged radiallyfrom said coolant channels is redirected as required to reach saidopening, and

3. liquid collection means located in the casing wall closely adjacentsaid trailing edge in register with said opening whereby open-circuitflow conditions are maintained with coolant fluid being dischargedradially from said coolant channels into said manifolds, redirected anddischarged from said first manifold through said opening into the hotmotive fluid flow with excess liquid being thrown into said collectionmeans.

2. The improvement of claim 1 wherein each of the manifolds consists ofa slot formed in the bucket core and extending from leading edge totrailing edge, the two slots being interconnected near the opening by apassage extending through the separating bucket core material.

3. The improvement of claim 1 wherein the opening is in the trailingedge of the bucket.

4. The improvement of claim 1 wherein the opening is through the top ofthe bucket near the trailing edge.

5. The improvement in claim 1 wherein the root of each bucket is in theform of a plurality of spaced tines fitting between and bonded to thewalls of annular grooves in the outer rim of the turbine disk.

1. In a gas turbine wherein a turbine disk is mounted on a shaft rotatably supported in a casing, said turbine disk extending substantially perpendicular to the axis of said shaft and having turbine buckets and platform means affixed to the outer rim thereof, said buckets receiving a driving force from a hot motive fluid confined within said casing and moving in a direction generally parallel to said axis of said shaft and the driving force being transmitted to said shaft via said turbine disk, means located radially inward of said platform adjacent said turbine disk for introducing liquid coolant within said turbine in a radially outward direction into open-circuit distribution paths by which said coolant traverses surface area of said rim and said platform means, passes into cooling channels in said buckets and exits from said channels in a radially outward direction, the improvement comprising: a manifolding, discharge and collection system for the coolant fluid exiting from the coolant channels in the turbine buckets, said system consisting of
 1. first and second interconnected manifolds located beneath the bucket surface near the tip of each bucket in flow communication with the discharge ends of the coolant channels, said first and second manifolds being located on the pressure and suction sides of said bucket, respectively,
 2. a single opening through the blade structure interconnecting said first manifold and the region of hot motive fluid flow within the casing near the trailing edge of said bucket, each of said manifolds being separated from the tip of said bucket by a wall formed in the bucket structure on the radially outward side of said manifold and extending generally chordwise of said bucket whereby coolant discharged radially from said coolant channels is redirected as required to reach said opening, and
 3. liquid collection means located in the casing wall closely adjacent said trailing edge in register with said opening whereby open-circuit flow conditions are maintained with coolant fluid being discharged radially from said coolant channels into said manifolds, redirected and discharged from said first manifold through said opening into the hot motive fluid flow with excess liquid being thrown into said collection means.
 2. a single opening through the blade structure interconnecting said first manifold and the region of hot motive fluid flow within the casing near the trailing edge of said bucket, each of said manifolds being separated from the tip of said bucket by a wall formed in the bucket structure on the radially outward side of said manifold and extending generally chordwise of said bucket whereby coolant discharged radially from said coolant channels is redirected as required to reach said opening, and
 2. The improvement of claim 1 wherein each of the manifolds consists of a slot formed in the bucket core and extending from leading edge to trailing edge, the two slots being interconnected near the opening by a passage extending through the separating bucket core material.
 3. The improvement of claim 1 wherein the opening is in the trailing edge of the bucket.
 3. liquid collection means located in the casing wall closely adjacent said trailing edge in register with said opening whereby open-circuit flow conditions are maintained with coolant fluid being discharged radially from said coolant channels into said manifolds, redirected and discharged from said first manifold through said opening into the hot motive fluid flow with excess liquid being thrown into said collection means.
 4. The improvement of claim 1 wherein the opening is through the top of the bucket near the trailing edge.
 5. The improvement in claim 1 wherein the root of each bucket is in the form of a plurality of spaced tines fitting between and bonded to the walls of annular grooves in the outer rim of the turbine disk. 